1. Field of the Invention
Exemplary aspects of the present invention relate to an image forming apparatus and an image forming method, and more particularly, to an image forming apparatus for forming a toner image by transferring the toner image onto a recording medium directly or indirectly via an intermediate transferor and an image forming method employed by the image forming apparatus.
2. Description of the Related Art
Related-art image forming apparatuses, such as copiers, facsimile machines, printers, or multifunction printers having at least one of copying, printing, scanning, and facsimile functions, typically form an image on a recording medium according to image data. Thus, for example, a charger uniformly charges a surface of a photoconductor; an optical writer emits a light beam onto the charged surface of the photoconductor to form an electrostatic latent image on the photoconductor according to the image data; a development device supplies toner to the electrostatic latent image formed on the photoconductor to render the electrostatic latent image visible as a toner image; the toner image is primarily transferred from the photoconductor onto an intermediate transfer belt and secondarily transferred from the intermediate transfer belt onto a recording medium; finally, a fixing device applies heat and pressure to the recording medium bearing the toner image to fix the toner image on the recording medium, thus forming the image on the recording medium.
In order to form a toner image having a desired toner density, a toner patch is formed on the photoconductor, which is transferred onto the intermediate transfer belt. An optical sensor disposed opposite the intermediate transfer belt detects the toner density of the toner patch based on which image forming conditions such as the toner density of the toner image, the charging bias, and the development bias are adjusted. For example, if the image forming apparatus receives a multiple print job for forming a toner image on a plurality of recording media, the toner patch is created in a gap between successive toner images formed on the intermediate transfer belt. The toner image primarily transferred from the photoconductor onto the intermediate transfer belt is secondarily transferred onto the recording medium conveyed through a secondary transfer region formed between the intermediate transfer belt and a secondary transfer device pressed against the intermediate transfer belt. Since the toner patch should not be transferred onto the recording medium, no recording medium is conveyed through the secondary transfer region as the toner patch passes through the secondary transfer region. Accordingly, the toner patch created on the intermediate transfer belt may contact the secondary transfer device as it is conveyed through the secondary transfer region due to absence of the recording medium and toner may move from the toner patch to the secondary transfer device. Hence, as a subsequent recording medium is conveyed through the secondary transfer region, the toner may further move from the secondary transfer device to the back side of the subsequent recording medium that contacts the secondary transfer device, staining the subsequent recording medium.
To address this problem, a sensor disposed upstream from the secondary transfer region in a recording medium conveyance direction may detect absence of a recording medium conveyed toward the secondary transfer region. Whenever the sensor detects such absence of the recording medium, the secondary transfer device separates from the intermediate transfer belt so that the toner patch created on the intermediate transfer belt does not come into contact with the secondary transfer device as it is conveyed through the secondary transfer region, thus preventing adhesion of toner of the toner patch to the secondary transfer device.
However, since the secondary transfer device separates from the intermediate transfer belt whenever the sensor detects absence of the recording medium, the secondary transfer device comes into contact with and separates from the intermediate transfer belt repeatedly during the multiple print job for forming the toner image on the plurality of recording media. Since it takes time to bring the secondary transfer device into contact with and isolation from the intermediate transfer belt, an increased time may be consumed to finish the multiple print job, degrading productivity of the image forming apparatus.
To address this problem, the secondary transfer device may move with respect to the intermediate transfer belt at an increased speed. However, the secondary transfer device moving at the increased speed may vibrate the intermediate transfer belt, degrading the toner image formed on the intermediate transfer belt.